Russian opposition figure Alexei Navalny is unconscious in hospital with suspected poisoning, his spokeswoman has said.

The anti-corruption campaigner fell ill during a flight and the plane made an emergency landing in Omsk, Kira Yarmysh said, adding that they suspected something had been mixed into his tea, writes BBC.

A hospital source confirmed treatment for poisoning to the Tass news agency.

Navalny, 44, is a staunch critic of President Vladimir Putin.

In June he described a vote on constitutional reforms as a “coup” and a “violation of the constitution. The reforms allow Vladimer Putin to serve another two terms in office.